A flange joint using a flange (i.e., a disk-like larger-diameter portion formed at an end of a pipe) has hitherto been known as a joint for a location where pipes for feeding fluids need to be removed in some cases. When connecting flanges to each other, a seal (gasket) is held between two flanges to prevent leakage of a fluid or intrusion of foreign matters from the outside. The gasket is mainly made of an elastic body and is fitted under compression into a groove that is formed in each of the flanges. Due to a repulsive force generated from the compressed gasket, the gasket is press-contacted with a wall surface of the groove, thus developing a sealing (enclosing) action.
In the case of feeding fluids (e.g., foods and pharmaceuticals) that require sanitary (hygienic) conditions, if a level difference (e.g., a recess or a projection) occurs in a pipe seam portion (particularly a gasket portion), the fluid accumulates in such a portion, and the sanitary conditions are no longer kept. Several proposals have been made to cope with the above-mentioned problem (Patent Documents 1 and 2).
Patent Document 1 discloses a pipe member connecting device for connecting and fixing respective connected ends of pipe members by joining the connected ends to each other with a ring-shaped packing interposed therebetween, and by tightening the connected ends with a clamp hand wound over an outer periphery of a joined portion, wherein both the tube members have annular abutment portions, which are formed at the connected ends of the pipe members and which are shaped such that, upon tightening with the clamp hand, the annular abutment portions are directly contacted with each other over entire circumferences thereof in a pipe axial direction and are engaged with each other in concave-convex relation, and the ring-shaped packing is placed in an annular recess formed in one of the connected ends on the inner peripheral side than the annular abutment portions, and is set such that the ring-shaped packing is brought into a compressed state when the annular abutment portions are directly contacted with each other, and that, in the compressed state, an inner periphery of the ring-shaped packing is substantially in flush with inner peripheral surfaces of both the pipe members.
Patent Document 2 discloses a flange coupling structure including flanges each having an end surface, which extends in a direction of radius thereof substantially perpendicular to an axis of a pipe, and each joined to a pipe end, a central circular opening penetrating through the end surface of the flange to be communicated with the inside of the pipe, and a device for fastening the flanges to each other in a state aligned in the axial direction, wherein the flange coupling structure comprises a seal chamber defined by an annular recess that is circumferentially formed around the central circular opening of the flange, and that is recessed inward in the axial direction, and an elastic seal ring positioned in the seal chamber and compressed in the seal chamber, the seal chamber and the elastic seal ring being dimensioned such that sealing pressure is generated from a wall surface of the seal chamber when flange sealing surfaces are directly engaged with each other.